The present invention relates a four-stroke-cycle engine of an outboard motor provided with a mechanism for adjusting or varying a valve timing.
In general, a four-stroke-cycle engine to be mounted on an outboard motor is fabricated into a vertical type in which a crankshaft and a camshaft are disposed in an upright state in the engine. A camshaft driving mechanism for transmitting a rotational motion of the crankshaft to the camshaft is disposed on an upper or lower surface of the engine. The camshaft driving mechanism includes a chain, a belt or a gear train.
The four-stroke-cycle engine is provided on its lower side with an oil pan so that oil reserved therein can be pumped out by means of oil pump to supply the oil to respective portions to be lubricated in the engine. The oil pump is usually disposed on the lower surface of the engine so that rotation of the crankshaft or camshaft is transmitted to the oil pump through an oil pump driving mechanism.
A mechanism for adjusting or varying the valve timing, hereinlater called xe2x80x9cvalve timing adjusting mechanismxe2x80x9d, which has already used widely in an engine for a vehicle such as an automobile and a motorcycle, has recently been used also in the four-stroke-cycle engine of an outboard motor. Such a mechanism shifts a rotational phase angle of the camshaft, which rotates at half (xc2xd) rotational speed of the crankshaft, in an advance angle direction in a high-revolution range rather than a low- or middle-revolution range, to provide appropriate valve timing all over the rotational range. The valve timing adjusting mechanism is provided on the end of the camshaft.
The valve timing adjusting mechanism is actuated through the oil supply from the oil pump. The oil pumped out by means of the oil pump is supplied first to a valve timing controlling mechanism and then to the valve timing adjusting mechanism. The valve timing controlling mechanism is disposed in the vicinity of the engine body so as to be connected to the valve timing adjusting mechanism.
However, in addition to a large size of the four-stroke-cycle engine, since many devices such as the camshaft driving mechanism, the oil pump, the oil pump driving mechanism, valve timing adjusting mechanism and the valve timing controlling mechanism are disposed on the engine body, as well as additional disposition of a gas-liquid separation chamber for a an intake system (including an air cleaner) having a prescribed volume, the entire structure of the engine is made inevitably large, providing a significant disadvantage for the structure of the outboard motor, and hence, it is required to provide a four-stroke-cycle engine of the outboard motor having a compact structure.
In addition, in the conventional structure of the engine, the valve timing controlling mechanism is placed so as to be apart from the engine body, and therefore, there increase the length of an oil passage between the oil pump and the valve timing controlling mechanism and the length of the other oil passage between the valve timing controlling mechanism and the valve timing adjusting mechanism, thus increasing passage loss of hydraulic (oil) pressure, which deteriorates the actuating response of the valve timing adjusting mechanism.
Furthermore, in the conventional structure, it is necessary to provide oil passages in the form of external piping, which are connected to the oil pump and the valve timing adjusting mechanism, on the valve timing controlling mechanism, which is placed apart from the engine body, thus increasing the number of necessary structural parts and the number of assembling steps, which involves cost increasing.
An object of the present invention is to substantially eliminate defects or disadvantages encountered in the prior art mentioned above and, therefore, to provide a four-stroke-cycle engine of an outboard motor, which makes it possible to improve the actuating response of the valve timing adjusting mechanism, to provide improved properties of layout-designing and downsizing of the engine and to reduce manufacturing cost.
This and other objects can be achieved according to the present invention by providing, in a general aspect, a four-stroke-cycle engine of an outboard motor, comprising:
an engine body;
a crankshaft disposed in an upright state in the engine body of the engine in an upright state;
at least one camshaft disposed in an upright state in the engine body;
at least one camshaft driving mechanism for transmitting a rotational motion of the crankshaft to the camshaft, the camshaft driving mechanism being disposed on a lower side of the engine body;
an oil pump for lubrication disposed on the lower side of the engine body;
at least one valve timing adjusting mechanism; and
at least one valve timing controlling mechanism to which an oil is to be supplied from the oil pump to control the valve timing adjusting mechanism, the valve timing controlling mechanism being disposed on a lower side of an outer wall of a valve train chamber in which the camshaft is received.
According to the structure of this general aspect of the present invention, the valve timing controlling mechanism is placed closely to the oil pump and the valve timing adjusting mechanism so as to decrease the length of an oil passage extending from the oil pump to the valve timing controlling mechanism as well as the length of an oil passage extending from the valve timing controlling mechanism to the valve timing adjusting mechanism, thus reducing passage loss of oil and improving the actuating response of the valve timing adjusting mechanism.
In addition, according to this aspect, it is unnecessary to provide the valve timing controlling mechanism with any oil passages in the form of external piping, which are connected to the oil pump and the valve timing adjusting mechanism. Accordingly, it is possible to form the oil passages within the engine so as to provide improved properties of the layout-designing and downsizing of the engine, thus decreasing the number of necessary structural parts and the number of assembling steps.
In a preferred embodiment of the above aspect, the valve timing adjusting mechanism is disposed on a lower end side of the camshaft and below the camshaft driving mechanism.
According to this feature, it is possible to make effective use of a space below the engine so as to provide the more improved properties of the layout-designing and downsizing of the engine and to reduce the distance between the valve timing adjusting mechanism and the valve timing controlling mechanism so as to remarkably improve the actuating response of the valve timing adjusting mechanism.
In a preferred embodiment, the four-stroke-cycle engine further comprises an intake device including a gas-liquid separation chamber, which is disposed on an upper side of the engine body.
According to this feature, the gas-liquid separation chamber and the valve timing adjusting mechanism are disposed on the upper and lower sides of the engine, respectively, to thereby cause no spatial interference with each other, thus providing the improved properties of the layout-designing and downsizing of the engine.
In a further preferred embodiment, the engine is a double-over-head-camshaft (DOHC) type engine, at least one camshaft comprises first and second camshaft members, the camshaft driving mechanism is configured so that the rotational motion of the crankshaft is transmitted to the first camshaft member through a chain and a rotational motion of the first camshaft member is transmitted to the second camshaft member through a gear train; the valve timing adjusting mechanism is disposed on a lower end of the first camshaft to be driven by a chain; the oil pump and an oil pump driving mechanism are disposed in a region on a side opposite to the first camshaft member to be driven by a chain relative to an axial line of a cylinder of the engine in a plan view; and a rotational motion of the second camshaft member to be driven by a gear is transmitted to the oil pump through the oil pump driving mechanism.
According to the additional features, the valve timing adjusting mechanism provided on the camshaft to be chain-driven can substantially be leveled with the oil pump and the oil pump driving mechanism, which are provided on the camshaft to be gear-driven in a side view of the engine, thus making effective use of the space below the engine and providing the more improved property of downsizing the engine.
In a further preferred embodiment, the engine is a double-over-head-camshaft and V-type engine having a V-shape bank in a plan view and the valve timing adjusting mechanism is disposed for the camshaft disposed inside the V-shape bank. Further, at least one camshaft may comprise first and second pairs of camshaft members, the first pair of camshaft members comprising a first inner camshaft member and a first outer camshaft member, which are disposed in a first bank of the V-type engine, and the second pair of camshaft members comprising a second inner camshaft member and a second outer camshaft member, which are disposed in a second bank of the V-type engine, the first and second inner camshaft members being located between the first and second outer camshaft members in the plan view, and the at least one valve timing adjusting mechanism comprises first and second valve timing adjusting devices provided for the first and second inner camshaft members, respectively.
According to such additional features, the valve timing adjusting mechanism having a relatively large diameter is placed in the inner side in the lateral direction of the engine, to thereby reduce the entire width of the engine, thus providing the more improved property of downsizing the engine.
It is to be noted that the nature and further characteristic features of the present invention will be made more clear from the following descriptions made with reference to the accompanying drawings.